Metal corrosion

Why metals corrode

All metals have a propensity to corrode due to their nature and manufacturing process. During manufacture (smelting) a great of energy in the form of heat is transferred to the metal.

During cooling, this has the effect of changing the micro-structure of the metal and creating microscopic areas of ‘difference’ within the metal. In iron, the micro-structure consists mainly of ferrite and pearlite.

In the presence of an electrolyte reactions take place between the ferrite and the pearlite, these reactions result in wastage of the ferrite and the formation of rust at the sites of the pearlite. The sites of the ferrite are known in corrosion parlance as ‘anodic’ sites and the pearlite locations are known as ‘cathodic’ sites.Metal corrosion always takes place at the anodes and corrosion products (rust) form on the cathodes. (See rust prevention)